The present invention generally relates to the field of data processing, particularly to link aggregation, and more particularly to an apparatus and method for asymmetrical link aggregation.
Link aggregation refers to various methods that combine a plurality of parallel network links together to increase the bandwidth dramatically over a single link and to provide redundancy in an event of link failure. These methods include the Link Aggregation Control Protocol (LACP) for Ethernet defined in IEEE 802.1ax and a number of proprietary solutions.
For example, in the link aggregation of IEEE 802.1ax, a plurality of physical links between a plurality of ports of two participating systems may be aggregated and represent a single logical link for each of the systems. The traffic on this logical link is distributed among the available physical links according to a distribution algorithm. Such a logic construct can avoid the participating systems sending any frame back into the logical link, thus breaking the loop that actually exists.
To further increase the bandwidth and system resilience, it is proposed that not only a plurality of physical links between a plurality of ports of one pair of systems may be aggregated together, but also a plurality of physical links between a plurality of ports of a plurality of pairs of systems may also be aggregated together. For example, in a data center, each access switch usually connects to two aggregation switches. Thus, the two or more physical links between the access switch and the two aggregation switches may be aggregated, so as to further increase the bandwidth and provide redundancy. In this way, for example, if one aggregation switch fails, the access switch can still use the other aggregation switch and the physical link therebetween to communicate. Since there may also be a link between the two aggregation switches, a loop may be formed in the network topology. Therefore, the Spanning Tree Protocol (STP) running on the switches is used to block the connection on one side to break the loop. However, this will reduce the available bandwidth between the access switch and the aggregation switches by 50%. FIG. 1 shows a schematic diagram illustrating using the STP to break the loop in the network topology formed by an access switch and two aggregation switches. As shown, an access switch connects to two aggregation switches. By using the STP on the switches, the connection between the access switch and one of the aggregation switches is blocked, thus reducing the available bandwidth between the access switch and the aggregation switches by 50%.
A number of implementations and methods have been proposed to provide full utilization of bandwidth while at the same time providing sufficient redundancy and resilience. Known solution include IEEE's distributed link aggregation group (DLAG) proposal, IBM System Networking's virtual link aggregation group (vLAG), Cisco's vPC, Arista Network's MLAG, Extreme Networks' M-LAG, etc.
These solutions all try to accomplish the above goal by running distributed link aggregation on the two aggregation switches to form an illusion of a single switch, at least from the point of view of the link aggregation partner. FIG. 2 shows a schematic diagram of distributed link aggregation. As shown, an access switch connects to two aggregation switches. By running a distributed link aggregation protocol among the access switch and the two aggregation switches, the two links between the access switch and the two aggregation switches appear to be a single link. That is, from the point of view of the access switch, the two links form a link aggregation group (LAG), while from the point of view of the aggregation switches, the two links form a distributed link aggregation group.
These solutions have the following drawbacks:
1. The approach of running distributed link aggregation involves various synchronization and switching when the “single switch” forms and breaks down. This greatly increases the complexity of the design, brings in additional processing load, and is probably problematic.
2. These solutions always impact the aggregation switches more than forming the illusion. For example, some solutions disable the MAC learning on the inter-switch link (ISL) when the illusion forms. This increases the complexity for the user to understand the whole affection and deploy the network.
3. It is almost impossible to have switches from different vendors form an illusion.
4. The illusion cannot extend to cross more than two aggregation switches.
It can be seen that there is a need for an improved solution of link aggregation in the field.